1. Field of the Invention
The present invention concerns a low-noise air blower unit that produces a stream of warmed air to inflate a thermal blanket.
2. Description of the Related Art
Augustine, et al. first described the use of temperature-controlled forced air to regulate the body temperature of patients, especially during and after surgery. U.S. Pat. No. 4,572,188, for example, used convective warming to prevent or treat hypothermia. In the '188 patent, temperature-controlled air is supplied by a blower unit that is connected to an airflow cover by a hose. In later-issued patents owned by the assignee of this application, the term "inflatable thermal blanket", synonymous with "airflow cover", is introduced. See, for example, U.S. Pat. No. 5,324,320, for "Thermal Blanket".
Inflatable thermal blankets assume a variety of shapes and sizes for specialized use, and include various inflatable structures that wrap around or drape over a patient. See, for example, U.S. Pat. Nos. 5,300,102 and 5,336,250. The mechanism fotr delivering heated air to a patient has also been expanded, beyond inflatable blankets, to include self-supporting tubes and plenums. See, for example, U.S. Pat. Nos. 5,300,101 and 5,350,417.
For ease of description, the various mechanisms for delivering a flow of temperature controlled air to bathe a patient are referred to herein as "thermal blankets." Patient-warming systems that use thermal blankets such as these may be collectively referred to as "convective warming systems." The basic convective warming system includes an air blower unit, a thermal blanket, and a flexible delivery hose connecting the two. These convective warming systems provide acknowledged clinical benefits. However, in certain situations, patients and medical personnel alike would benefit from having an air blower unit that operates as quietly as possible. Some patients, for example, may be sensitive to noise due to their particular medical conditions. Also, the operating room must be kept quiet to avoid distracting the operating team, and to aid the doctors and nurses in hearing vital sign monitors. Furthermore, quiet surroundings are desirable in post-operative recovery rooms to help patients gently emerge from anesthesia-induced sleep. Moreover, a reduced-noise air blower unit provides a competitive advantage in selling and marketing such units, whether for use in operating rooms, intensive care units, or a patient's hospital room.
FIGS. 1 and 2 illustrate the components of a typical air blower unit 100 (also "blower unit") in greater detail. The blower unit 100 includes a blower 102 powered by an electric motor 104. In many cases, the blower 102 comprises a squirrel cage blower. This type of blower typically has a short cylinder with a plurality of fan blades that are positioned around the circumference of the cylinder and oriented longitudinally. The blower 102 withdraws ambient air into all inlet 106 and creates an airstream that continues through an outlet 108. The outlet 108 is coupled to a tube 116 that connects to a thermal blanket 118 via a coupling ring 120. Filter media 110 may be provided proximate the inlet 106 to cleanse the ambient air. The stream of air created by the blower 102 is heated by a heater 112, which may comprise a resistive heating coil, receiving power from an electric power supply 114.
In operation, the blower unit 100 rests on the supporting surface 122, supported by feet or rollers 124. In this position, the blower 102 revolves about an axis of rotation 126. The blower 102 generates an airstream by drawing in air through the intake 106 in a direction 128 that is substantially parallel to the axis of rotation 126. The airstream flows through the intake 106 and is redirected by the blower 102 in a direction 130 that is substantially perpendicular to the axis of rotation 126. The airstream flows in the direction 130 out of the blower 102, through the heater 112 and out of the outlet 108 into the tube 116. In the prior art blower unit 100, the heater 112 is downstream of the blower 102, between the blower 102 and the outlet 108. The motor 104 is entirely out of the airstream, being neither upstream nor downstream of the blower 102.
Viewed differently, the vertical orientation of the axis of rotation 126 with respect to the air flow means that noise 132 will be emitted vertically upwardly, and noise 134 will be emitted parallel to the floor 122.
As mentioned above, known blower units would further benefit their users by operating with reduced noise. As an example, a significant amount of noise occurs as the airstream created by the blower 102 exits the unit 100 through the outlet 108. This airstream typically carries a measurable amount of noise generated by the motor 104 and the rotating blades of the blower 102. Since the airstream flows in the direction 130, so does the accompanying, noise 132. And, if the unit 100 rests upon the floor 122, the noise 132 will be projected upward 130 in the direction 130, toward the patient. Moreover, a significant portion of the noise 132 may be carried via the tube 116 directly into the blanket 118, as shown by the noise 136.
Another significant source of noise is found at the inlet 106 of the blower 102. In particular, some noise from the blower 102 and motor 104 projects outward through the inlet 106, opposite to the direction 128. Depending upon the placement of the blower unit 100, this noise 134 may be projected directly at medical staff and patient.
One approach to reducing the noise of a convective warming system is found in U.S. patent application Ser. No. 08/383,880, filed Feb. 6, 1995, for "A Source of Inflating Medium With Active Noise Cancellation for an Inflatable Thermal Core Apparatus", which is assigned commonly with this application and incorporated herein by reference. Here noise reduction is achieved by positioning active cancellation elements in the blower hose. This approach, however, does not quiet the blower unit itself.
In view of these considerations, then, there is a manifest need for a blower unit that is compact and operates with reduced noise, while providing a regulated, thermally controlled airstream.